In recent years there has been demand for boilers for burning coals or heavy oils which redress the imbalance in the distribution of the air and the fuel fed to the burner, in order to decrease NOx and carbon monoxide (CO).
FIG. 3 is a horizontal sectional view illustrating a burner structure of a boiler. In this conventional structure, the burner 10 is a device for injecting the fuel and the air for combustion into a furnace 1 in the boiler. In FIG. 3, reference numeral 2 denotes a wall surface of the furnace, and reference numeral 3 denotes a water-cooled wall formed on the wall surface 2 of the furnace on the side toward the furnace. The burner 10 that is shown is disposed at a corner of the boiler.
The burner 10 includes a wind box 12 forming an air flow passage 11 for injecting the air for combustion into the furnace 1, and a fuel pipe 20 for injecting the fuel into the furnace 1. A fuel nozzle 21 is provided at the tip of the fuel pipe 20. An air nozzle 22 which communicates with the air flow passage 11 in the wind box 12 is provided around the outer circumference of the fuel nozzle 21. A fuel such as coal or heavy oil together with primary air is ejected from the fuel nozzle 21. Secondary air (air for combustion) is ejected from the air nozzle 22.
Due to limitations imposed on the arrangement and passage in order to downsize the boiler, the air flow passage 11 formed in the wind box 12, in many cases, has a bent portion 13 that is, usually, greatly bent by not less than 90° just before joining with the furnace 1. In the bent portion 13, separation and drift occurs in the stream of the air for combustion. Therefore, a structure has been employed in which a guide vane 14 is disposed in the air flow passage 11 in the wind box 12 in order to prevent the separation and drift. Reference numeral 15 in FIG. 3 denotes a damper provided in front (upstream) of the guide vane 14 to adjust the flow rate of the air for combustion.
In conventional art related to combustion in boilers, disparity among burner ports or among air inject ports is reduced, or conversely, the bias is reinforced (e.g., see patent citation 1).
Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 7-12310